The present disclosure relates, in various exemplary embodiments, to certain polycarbonate graft copolymers and articles formed from such graft copolymers. The graft copolymers exhibit properties such as high scratch resistance and/or high anti-fog properties. Also disclosed are methods for preparing and/or using the same.
Polycarbonates are synthetic thermoplastic resins derived from bisphenols and phosgene, or their derivatives. They are linear polyesters of carbonic acid and can be formed from dihydroxy compounds and carbonate diesters, or by ester interchange. Polymerization may be in aqueous, interfacial, or in nonaqueous solution.
Polycarbonate-based materials are used in a broad variety of applications because of their high transparency, clarity, heat resistance, ignition resistance, toughness, stability, impact resistance, creep resistance, and mechanical strength. Due to their optical quality, polycarbonates can be used in lighting applications including automotive headlamp lenses, covers and lenses for other optical devices, as well as transparent films and sheets. They can also be used in a wide variety of molded products such as medical devices, radio and TV bezels (i.e. grooved rims for holding glass or plastic panes such as lenses, tuning dials, and other indicating devices), mobile phone keypads, notebook computer housings and keys, optical display films, automotive parts, and other electronic and consumer products.
Scratch resistance is useful for articles whose exterior surface may be subject to physical contact by other objects. For example, everyday activities which can scratch an article may include sliding on a surface, dropping, and rubbing against other items such as coins or keys when placed in a pocket. Polymer compositions with scratch resistance are therefore desirable in articles requiring a durable surface finish and appearance.
In particular, polycarbonates based on bisphenol A (BPA) have limited scratch resistance. One method of preventing or minimizing scratch damage is to apply a hardcoat to an article formed from a BPA polycarbonate. This hardcoat requires another manufacturing step, adding additional cost to the article. Other disadvantages include durability and complexity.
Another method is to use a scratch-resistant material made from a copolymer of BPA and dimethyl bisphenol cyclohexane (DMBPC). However, these copolymers also have decreased impact properties and ductility compared to polycarbonates based on BPA.
BPA polycarbonate is also easily fogged by water condensing on cold surfaces with low surface tension. Fogging lessens the advantage of the optical properties of BPA polycarbonate.
One method of reducing or eliminating fog formation on the surface of BPA polycarbonate or other thermoplastics is to add an anti-fog coating. Another method is to use sulfonation techniques to introduce hydrophilic functionality on the molecules. However, both of these methods are inconvenient and expensive. Additionally, widely used anti-fog additives for polyolefins are either not thermally stable, not miscible with polycarbonate, or simply not effective in polycarbonate. Some additives become surface active only after conditioning under specific conditions. Others are miscible with polycarbonate, but reduce the glass transition temperature. Even where the additives are thermally stable and surface active, they may not be permanent due to the lack of chemical bonding between the additives and polymer matrices.
It would be desirable to provide a polycarbonate composition having improved anti-scratch and/or anti-fog properties. In particular, it would be desirable to provide such polycarbonates possessing these properties without the need for additional coating or post-mold treatments. The polycarbonate composition would be useful for certain transparent articles, such as optical parts, among other applications.